1. Field of the Invention
This invention relates to a method for generating a development drawing in which dimension of a solid form is changed according to an elongation amount presented when a sheet material is changed up to a target angle (including a spring-back) and entering a folding line taking into account the elongation amount into this development drawing.
2. Description of the Prior Art
FIG. 1 is a schematic structure diagram of a line control system for a bending machine. The line control system for the bending machine shown in FIG. 1 comprises a centralized station 1, CAE (computer-aided engineering) 2, automatic programming device 3 and NC (numeric control) apparatus 5 for controlling the bending machine 4, these components being connected through a LAN (local area network).
In this system, a processing program (also called NC program) for producing a desired product by bending is created by the automatic programming device 3 and filed in the centralized station 1 corresponding to processing schedule.
Then, the centralized station selects a processing program of a product which has reached a date of scheduled production from a processing schedule and transmits it to the NC apparatus 5 so as to operate the bending machine 4.
When the sheet material is bent using the bending machine 4, as shown in FIG. 2, the sheet material 7 (hereinafter referred to as workpiece 7) is placed on a die 9 while pressed against a back gauge 8 horizontally and a punch 10 is descended up to a target Di value so as to bend the workpiece 7.
At this time, the back gauge 8 is controlled so that when a tip 11 of the punch 10 makes contact with the workpiece 7, the tip 11 of the punch 10 is located on a bending line 12 (reach Li) of the workpiece 7.
It is known that with the aforementioned bending, the workpiece 7 is extended. Therefore, according to the prior art, when a processing program is created by an automatic programming apparatus 3, an operator enters a folding line into a development drawing according to a preliminarily prepared elongation amount table (punch type--material--bending angle--elongation amount) by operating the automatic programming apparatus 3.
However, when the operator enters a folding line taking into account an elongation amount, he must refer to the elongation amount table preliminarily prepared upon the entry. Thus, there is a possibility that the operator may enter the folding line into an improper position.
Although the elongation amount table is determined depending on punch type, material, bending angle and the like, there is not always prepared a punch and a die mentioned in the elongation amount table on a machine tool. In this case, bending is carried out using a substitute punch or a substitute die on the machine tool. Thus, even if the operator enters a folding line based on the elongation amount table, when a workpiece is actually processed, there is sometimes a case in which a desired product (dotted line) may be different from an actually produced product (solid line).